The Seismic Characteristics of the Ocean-Continent Transition (OCT) Across the Eastern Grand Banks Margin
Abstract
Coincident 2D multi-channel seismic (MCS) and wide-angle reflection/refraction seismic data were collected across the Eastern Grand Banks, the Flemish Cap and the Newfoundland Basin. The southernmost profile, Line 3, transects the full thickness continental crust beneath the shelf, the Jeanne d'Arc Basin, the Carson Basin, the Salar Basin, and it extends into the Newfoundland Basin north of the Newfoundland Seamounts. Our results show that the continental crust beneath the shelf, of ~35km thick, is comprised of 3 layers - upper (velocity = 5.8-6.2 km/s), middle (6.3-6.5 km/s) and lower crust (6.8-6.9 km/s). Crustal thinning that led to continental breakup was initially abrupt beneath the Carson Basin and then more gradual seaward beneath the Salar Basin and the Newfoundland Basin. This formed a wide zone (~100 km) of very thin (<8km) continental crust sitting on a layer of serpentinized mantle (7.5-8.0km/s). Only the upper crust exists across the seaward most 50 km of this zone and may be a result of a westward dipping detachment fault. The crust-mantle boundary at the landward end of the serpentinized mantle layer coincides with a prominent landward dipping reflector, similar to the "L-reflector" previously observed on Lithoprobe profile 85-2 across the SE Grand Banks. Beyond where the tilted fault blocks cease to exist, an ocean-continent transition (OCT) zone ~75km wide consists of extremely thin (~5km) and unreflective basement layer with high velocity gradient (4.5-7.7 km/s). Such properties are consistent with either exhumed mantle or ultra-slow spreading oceanic crust. The serpentinized mantle layer that underlain the thin continental crust extends seaward beneath this basement layer, making a total width of ~200km and a lower boundary depth of ~15km. The serpentinized mantle layer pinches out seaward where seafloor spreading formed normal oceanic crust. Similar mantle layers of different widths were observed across the E. Flemish Cap margin and the SE Grand Banks. Although the widths and detailed structures of crustal zones vary along the eastern Grand Banks margin, serpentinized mantle exists across the OCT and might have been exhumed, as was suggested by recent ODP drilling results north of Line 3 (Leg 210) and in the conjugated Iberia margin (Leg 149 and 173).
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.T32B..04L
- Keywords:
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- 3025 Marine seismics (0935);
- 3040 Plate tectonics (8150;
- 8155;
- 8157;
- 8158);
- 8105 Continental margins and sedimentary basins;
- 8109 Continental tectonics: extensional (0905)